The present invention relates to interference fit ups and, more particularly, to a method for achieving interference fit ups, such as for high pressure turbine hangers for a gas turbine engine. The application is related to co-pending commonly assigned application, Ser. No. 07/702,549, filed May 20, 1991, the disclosure of which is incorporated by reference herein.
Interference fit ups of high pressure turbine (HPT) components is a method of locating and holding parts in the engine. Typically, this type of fit up is accomplished for segmented parts by a procedure known as dimpling. In this procedure, a dimple is put into a part by deforming a flat section by pulling the material, which can be accomplished by any suitable means, such as hydraulically. In this pulled region, the material is plastically deformed into a mound shape, resulting in the term dimple. Necessary loads for achieving this type of deformation are dependent upon material thickness. For example, for material which is in the region of 0.1 inches, a typical load is in the 5000 lbf range.
This dimpling procedure is used for fit ups on segmented high pressure turbine shroud hangers to locate and restrain them in the 360.degree. support structure of the hanger. Dimples are located on both the forward and aft rails of the hanger and are toleranced to achieve an interference fit with the support structure. The hanger is then essentially forced to lodge in the support with typical interference ranges being from line to line to 0.004 inches maximum.
Unfortunately, the force used to lodge the hanger in the support deforms the material of the hanger, compromising component mechanical integrity. Sensitivities arise in the material as a result of the reduction and destruction of the material properties and capabilities, affecting the form, fit, and function of the component. Additionally, the elastic properties of the material are destroyed by the plastic deformation. Finally, when the rails are removed during maintenance, it is difficult to reproduce the interference requirements for continued engine operation, requiring the expense of either reworking or replacing parts.
It is seen then that there exists a need for an interference fit up of components which does not compromise component mechanical integrity and the form, fit, and function of the component, particularly a fit up which would reduce part cost.